This invention relates to a flat cathode ray display tube comprising an envelope having a front wall comprising a flat, optically transparent faceplate carrying a screen and a rear wall opposite the front wall, means for producing an electron beam disposed adjacent the rear wall, the electron beam producing means being arranged to direct an electron beam substantially parallel to the faceplate and over the rear wall of the envelope, a reversing lens which turns the electron beam so that it travels in the opposite direction parallel to the faceplate, a deflector arrangement for deflecting the turned beam towards the screen, and getter means located in the envelope.
A flat display tube generally of this kind is described in published British Patent Application No. 2101396A corresponding to U.S. patent application Ser. No. 830,388, filed Feb. 14, 1986 (PHB32794). In this tube, the envelope volume is divided into front and rear portions by a partition extending parallel to the faceplate, the electron beam being directed initially parallel to and over one side of the partition and then reversed by the reversing lens to travel parallel to the other side of the partition, this other side carrying a beam deflection electrode arrangement for field scanning. The tube also includes a further beam deflection electrode arrangement adjacent the electron beam producing means, namely an electron gun, in the rear envelope portion which serves to deflect the beam in a plane parallel to the partition and the faceplate to achieve line scanning, and a channel plate electron multiplier disposed closely adjacent and parallel to the screen for current multiplying the electron beam following deflection by the deflection electrode arrangements.
As is customary with cathode ray display tubes, getter means are contained within the envelope, although such means are not specifically referred to in the aforementioned published British Patent Application No. 2101396A. It is an important consideration in the locating of the getter means that upon activation thereof sensitive operating components within the envelope are not contaminated by material emanating from the getter means. Heretofore, the getter means has been disposed in the region of the electron gun. In order to prevent the electron gun from becoming contaminated by material from the getter means upon its activation, such contamination being likely to impair performance of the gun, a separate barrier member is mounted in the envelope and used to shield the electron gun, the member being located intermediate the getter means and the electron gun and serving to prevent material emitted by the getter means and travelling directly towards the gun from reaching the gun.
The provision of such a barrier member is not entirely satisfactory and has a number of disadvantages. Although it is relatively simple to fabricate, its fabrication and securement in the envelope nevertheless adds to the overall time taken to construct the tube and increases the number of components involved. Furthermore, it will be appreciated that the amount of available space within the envelope is minimal and the provision of this additional component takes up valuable space. Besides complicating the assembly of the internal components of the tube, the provision of a barrier member further requires that other components be arranged to allow for its accomodation.
It is an object of the present invention to provide a cathode ray display tube of the above kind including getter means disposed in its envelope but in which the aforementioned disadvantages associated therewith are avoided.